This invention relates to a mobile cellular telephone comprising a GPS receiver.
It is known to provide a mobile cellular telephone with a GPS receiver for the purpose of enabling operators of cellular telephone networks to determine the location from which a call is made. Conventionally, this occurs by a network operator making a location request to the telephone via a telephone network base station; and in response to the request, the telephone powering up its GPS receiver to determine its location and transmitting information corresponding to its location back to the base station.
In such a telephone, the power consumption of the GPS receiver during GPS signal acquisition and tracking, and navigation processing can be high. Therefore, as a mobile cellular telephone typically has a finite battery capacity, it is preferable that the GPS receiver is powered up only when required. The battery capacity problem is further compounded by the fashion for the miniaturisation of mobile telephones (and their battery packs) for both aesthetic and ergonomic reasons.
For an emergency call to the emergency services, it is of course desirable for the call location to be available as soon as possible. However, from a xe2x80x9ccold startxe2x80x9d where the GPS receiver does not have access to up to date ephemeris data or even worse from a xe2x80x9cfactory cold startxe2x80x9d where the GPS receiver does not have an up to date almanac, the time to first fix (TTFF) can be anywhere between 30 seconds and 5 minutes.
In order to reduce the TTFF, a GPS receiver may be provided with base station assistance in order to acquire GPS signals more quickly. Such assistance may include the provision by the base station to the receiver of a precision carrier frequency reference signal for calibrating the local oscillator used in the GPS receiver; the data message for up to date satellite almanac and ephemeris data from which Doppler shift for satellites in view can be determined; and the current PRN code phase. With such assistance, it is possible to sweep only a narrowed range of frequencies and code phases in which the target PRN code is known to occupy, thereby reducing the number of code instances that need to be checked and thus reducing the time for code acquisition, in fact to as little as a few seconds. Base station assistance is further described in U.S. Pat. Nos. 5,841,396 and 5,874,914 which are incorporated herein by reference.
Not withstanding the above improvement, it is desirable to further reduce the TTFF. It is also an object of the present invention to do so.
According to the present invention, a mobile cellular telephone is provided comprising a communications transmitter and receiver arranged for two-way communication with a base station, and a GPS receiver characterised in that the GPS receiver is arranged to power up in response to direct interaction between a user and the mobile phone after the telephone has been switched on.
Such a GPS receiver is able to immediately commence processing GPS signals in order to retrieve the pseudorange information and determining its current position, without waiting for call connection or a location request transmitted from a base station. This is beneficial in that GPS processing prior to call connection reduces the risk of signal interference and drowning of the GPS signal caused by the mobile unit""s transmitter transmitting encoded voice or other data to a base station and perhaps also caused by the mobile unit""s receiver receiving base station replies.
Furthermore, as powered up only when required, the overall power consumption of the GPS receiver (and therefore the telephone) remains relatively low.
In particular, but not exclusively, the GPS receiver may be arranged to power up in response to the user making a particular call, for example, to the emergency services.
In such an arrangement, recognition by the telephone of a particular call being made may occur when the user enters the call telephone number, for example, by typing on a keypad or using speech recognition.
Alternatively, recognition may occur when the user enters one or more, but not all of the digits of the call telephone number. In such an event, the GPS receiver may be arranged to power down should that the number being entered by the user deviate from the call telephone number, thus saving power.
As an alternative to call recognition, the GPS receiver may be arranged to power up in response to a change in the strength of the signals received from a base station of a cellular radio transmission system, e.g. indicative of the mobile telephone being removed from a pocket or briefcase; to detected movement of the mobile telephone, e.g. when detected by an accelerometer located in the mobile telephone; a change in temperature of the telephone or pressure applied to the telephone, indicative of handling by the user; or to the retracting of a cover on the mobile telephone, e.g. in the case of a mobile telephone with a sliding cover protecting the key pad, by retracting the cover, or in the case of a xe2x80x9cflip topxe2x80x9d mobile telephone, by flipping the cover. The GPS receiver may be arranged to power up in response to a combination of these features, possible determined by fuzzy logic.
For an Internet enabled mobile telephone with a GPS receiver, the GPS receiver may be arranged to power up in response to the user selecting a particular web site, for example, a website associated with a location based service whereby the call location is determined in anticipation of a request from that website.